A thermal molding sheet can be widely used from small molded products, like packaging containers such as food containers, to large molded products, like structural members such as housing equipment members, by thermal molding such as vacuum molding, pressure molding, vacuum-pressure molding, and double-side vacuum molding. As properties required for the packaging containers, appearance properties such as transparency and gloss, and properties such as heat resistance and oil resistance, for example, when heating and cooking contents in a microwave oven, are required. Further, in recent years, attention to environmental problems has increased, and thus polypropylene-based resin sheets are preferred to amorphous resin sheets such as polystyrene and ABS which are excellent in thermal moldability. In addition, as properties required for the structural members, mechanical properties such as rigidity, strength and heat resistance are required to be excellent, and moldability such as draw down resistance and spreadability are required to be excellent as well.
As a polypropylene-based resin for a sheet used for manufacturing a molded product by a thermal molding method, a propylene homopolymer and a propylene-α-olefin random copolymer are often used from viewpoints of moldability, product rigidity, transparency or the like. However, the above resins are low in melt tension, and not sufficient in draw down resistance when in thermal molding of sheets, so that an improvement is required.
In order to improve the draw down resistance, a resin composition containing a polypropylene resin having a long-chain branch structure has been proposed (see, for example, Patent Document 1). However, with this composition, the draw down resistance may be not sufficient when a thick and large molded product is thermal molded.
Further, since large molded products usually have complicated shapes, sheets are also required to have good spreadability when in thermal molding. Polypropylene-based resins used for conventional thermal molding are not sufficient in spreadability, and even if the polypropylene resins can be shaped into a complicated shape, a molded article is obtained by non-uniform spread, so that the molded article has a large uneven thickness and is prone to buckling and breaking. Therefore, it is difficult to satisfy reliability higher than that required for the structural members. As for such structural members, a thermal-molded article made of ABS or polystyrene, which is an amorphous resin, has been widely used (see, for example, Patent Document 2).